The present invention relates to a cleaning device for magnetic recording tape drives and, more specifically, to a mechanically actuated head cleaner for small size linear magnetic recording cartridge tape drives.
In magnetic tape drives the recording media is moved from a supply spool in a tape cartridge to a take-up spool on the tape drive across a head that holds the recording and read-back elements. When the tape cartridge is to be removed the tape is rewound back onto the supply spool. The path of the tape is defined by guiding elements including rollers, hydrodynamic bearings, hydrostatic bearings, and other similar components. In prior art systems with hydrodynamic bearings an air pump to pressurize the bearings is also needed. Pressurized bearings separate the tape from the bearings by a thin film of air, reducing wear on the tape and extending tape life.
The tape must also be maintained above the head a given height. The distance of the tape from the head, known as the xe2x80x9cflying heightxe2x80x9d, must be precisely controlled during recording and read-back of data. The ability to record and read-back data is lost if the flying height exceeds certain limits. In the older systems the air pump supplies pressurized air through an electrically activated valve to the surface of the recording head to separate the tape from the head when the movement of the tape is stopped. The airflow is turned on when tape movement is stopped, as well as when tape is accelerated or decelerated. When tape movement is at normal speed the pressurized air is turned off because the movement of the tape generates a thin film of air that separates the tape and the recording surface. Slots in the surface of the recording head are used to bleed off excessive air so that the separating air film is kept thin.
In operation the tape is moved past the head and data is encoded on to the tape. All heads have a writing portion and a reading portion immediately following. The reading portion reads the data just written on the tape and compares it to the original data to check for errors. All drives have built in microprocessors to check the error rate. The microprocessor will generally send an error message to the operator when a set error rate is exceeded so that the head can be cleaned.
The recording portion of the head is not writing on the whole width of the tape, only a fraction of the width is used in any one pass of the tape across the head. The head can move laterally back and forth across the width of the tape to allow the head to write on a given fraction of the width of the tape. The controls of the tape drive move the tape backward and forward as the head moves, resulting in the data being deposited in a serpentine path on the tape.
Although there are many different types of tape drives on the market they all have some common characteristics. In response to the requirements of the users, tape drives are becoming smaller, less costly, and they store increasing amounts of data. Air pumps and filters are too large and expensive to be used in the new, smaller tape drives.
Today even high-end tape drive manufacturers can no longer afford air pumps. Without the aid of pressurized air, the air-film above the surface of the recording head collapses when tape decelerates from the nominal speed during a stop operation. The tape then comes in direct contact with the head while the tape is still moving. Similarly, at the beginning of a start operation the tape starts to move while still in direct contact with the head. This contact with the head results in increased debris on the head as loose particles are scraped off the tape and deposited on the head.
Contamination of the head is undesirable for two reasons. First, when debris collects in the above-described slots in the head the air generated by the movement of the tape can no longer move away from the surface. The flying height increases and the ability to record or read back data is lost. Second, because of the increased recording density of modern systems, even small particles of debris on the tape will result in data errors. As the tape comes in contact with the head the debris can be transferred to the tape, increasing the number of errors.
A number of patents have addressed the issue of cleaning either the recording media or the head. A number of them are discussed herein. Most prior art patents relate to helical scan recorders where a recording head is mounted on a rotary drum. U.S. Pat. Nos. 5,335,128; 5,386,333; 5,453,894 and 5,701,224 all describe a mechanism that moves a cleaning roller to the spinning head. U.S. Pat. No. 4,704,647 uses a pad instead of a roller, while U.S. Pat. No. 3,964,104 uses a rotary brush. These mechanisms can be effective in removing debris from the surface of a spinning head, but they cannot remove debris from a head in a linear tape drive containing grooves.
A means to remove debris from the tape itself is disclosed in U.S. Pat. Nos. 4,165,526 and 5,136,448. Other prior art discusses cartridges containing a special cleaning tape. U.S. Pat. Nos. 5,859,755 and 5,991,127 illustrate a cleaning tape that moves through the tape path and removes contamination from tape path components.
Cleaning cartridges and tape cleaners are successful in slowing down the buildup of debris in the head grooves, but these cleaning cartridges cannot entirely remove all the debris. Manual cleaning operations of the head by an operator are still required.
Several patents have attempted to address this problem by providing for automatic head cleaning devises. U.S. Pat. No. 5,930,089 discloses a mechanism that displaces the tape and moves a brush to the recording head. The cleaning operation is performed without removal of the data tape. The brush has totally separate components from the rest of the drive components to move the brush to the head. The normal operator finds any disruption of the recording process for cleaning purposes undesirable as this increases the time required for each back up operation. In addition, cleaning the head while the tape is next to the head increases the change that the tape will get dirty, necessitating cleaning the tape also. A preferred cleaning device would be able to clean the head sufficiently before a tape is loaded for an operation of the drive.
A mechanically actuated cleaning device that moves a brush across the head surface twice whenever a cartridge is loaded or unloaded is described in U.S. Pat. No. 5,793,580. The number of cycles performed during a cleaning operation is a function of the mechanical parts and therefore cannot be modified. Two cycles is a low number as debris on the head can at times be difficult to remove.
A device that can periodically thoroughly clean the head surface, including any slots in the surface, is needed. Due to the size and cost restrictions of the newer tape drives, such a device should not require any electrical circuits or actuators such as solenoids or motors. The device needs to be able to adjust the amount of cleaning based on the condition of the head. The present invention solves these problems by providing an automatic device to move a brush up to the head every time the tape cartridge is removed from the tape drive. The head is then moved against the brush using the head actuator, cleaning the head.
The primary aspect of the present invention is to provide an automatic device to clean the recording head of a tape drive.
Another aspect of the present invention is to provide a device that will adjust the amount of cleaning operations done on the recording head according to the state of the head.
Another aspect of the present invention is to provide an automatic head cleaner for a tape drive with the minimum necessary additional parts.
Other aspects of this invention will appear from the following description and appended claims, reference being made to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.
The present invention provides a mechanically actuated cleaning device for a linear magnetic tape drive that uses a tape cartridge. The tape drive consists of at least six elements: a recording head, an actuator attached to the head that moves the recording head across the width of the tape, a take-up hub, a supply hub, a mechanism to load the tape cartridge onto the supply hub, and a cleaning device.
The cleaning device contains at least three components: a brush, a housing for the brush, and a link to the loading device. The housing is attached through a mechanical link to the loading mechanism in such a manner that the brush is moved into contact with the head as the cartridge is removed from the take-up hub. When a cartridge is loaded onto the take-up hub, the motion of the loading device is used to shift the cleaning device away from the head to allow the tape to be moved across the surface of the head. The cleaning operation is performed after the cartridge is unloaded and before the next cartridge is loaded. The head actuator, normally used to access different areas of the tape, moves the head up and down several times while the brush is pushed against the head. Thus, debris is removed from the head. The number of cycles the head moves can easily be modified to fit the requirements. For example, if the number of bit errors after a write operation indicates a contaminated head, the number of cleaning cycles may be increased. A typical number is 10 to 16 cycles for normal operation, 24 to 32 cycles for highly contaminated heads.